The present invention relates to a method for correcting a measuring signal generated by an apparatus which measures in contact-free fashion by scanning a surface to be measured with a light beam and detecting light reflected from the surface with an opto-electronic detector. Typically, as the light beam crosses a point on the surface determined by a sighting line along which the opto-electronic sights, a pulse is created. When the beam reverses, a second pulse is created.
German Nos. OS1773635 and OS2533906 corresponding to U.S. Pat. No. 3,885,875, both incorporated herein by reference, show optical measuring systems wherein a reflected signal is received by an opto-electronic detector.
Given a known apparatus of the type above cited, a strongly concentrated light beam, preferably a laser beam moved back and forth in a plane, scans a surface of an object. An opto-electronic detector installation with a strongly concentrated receiving characteristic along a sighting line is so arranged that the sighting line is disposed in a plane and strikes the surface of the object at a location which is also struck by the strongly concentrated light beam being moved back and forth. The detector installation thus essentially receives only light which is scattered from the surface in the direction of the sighting line, and also only when the strongly concectrated light beam strikes the location.
The detector installation measures the overall intensity of the received light. The resulting measuring signal results from the convolution of the intensity distribution provided at the impact spot of the strongly conventrated light beam on the surface of the object with the diaphragm or slit function of the detector installation over time. Graphically this means that the light spot radiating in the direction of the sighting line, and existing light at the place of incidence of the light beam on the surface of the object, travels over time into the diaphragm aperture, so that increasingly more light passes through the diaphragm aperture until a maximum value is attained. Then the light spot over time again travels out of the diaphragm aperture. If the local intensity in this light spot is constant during the travelling-through time, then the detector installation emits a signal which under certain conditions exhibits a symmetrical chronological progression in the form of a bell shaped function. For example, this is the case if the diaphragm aperture is a rectangular slit which is swept perpendicularly to the longitudinal direction of the slit by a circular light spot of equal intensity everywhere.
Given the known installation, the measurement is based on the stated chronologically symmetrical progression of the measuring signal supplied by the detector installation.
If, therefore, the chronologically symmetrical progression of the electrical signal supplied by the detector installation is no longer provided, measuring errors occur with this installation. The chronologically symmetrical progression of the electrical signal is, for example, no longer guaranteed when the intensity of the light scattered by the surface of the object locally varies.